Directional boring apparatus or trenchless drills for making holes through soil are well known. The directional borer generally includes a series of drill rods joined end to end to form a drill string. The drill string is pushed or pulled though the soil by means of a powerful device such as a hydraulic cylinder. See McDonald et al. U.S. Pat. No. 4,694,913, Malzahn, U.S. Pat. Nos. 4,945,999 and 5,070,848, and Cherrington, U.S. Pat. No. 4,697,775 (U.S. Pat. No. RE 33,793). The drill string may be pushed and rotated at the same time as described in Dunn, U.S. Pat. No. 4,953,633 and Deken, et al., U.S. Pat. No. 5,242,026. A spade, bit or head having one or more angled faces configured for boring is disposed at the end of the drill string and may include an ejection nozzle for water or drilling mud to assist in boring.
In one known directional boring system, the drill bit is pushed through the soil without rotation in order to steer the tool by means of the angled face, which is typically a forwardly facing sloped surface. For rocky conditions, a row of teeth may be added to the drill bit and the bit operated in the manner described in Runquist et al. U.S. Pat. No. 5,778,991. Other toothed bits for directional boring through rock are shown in European Patent Applications Nos. EP 0 857 852 and EP 0 857 853, Cox U.S. Pat. No. 5,899,283, Skaggs U.S. Pat. No. 5,647,448 and Stephenson U.S. Pat. No. 5,799,740. Steering systems for use with these devices require keeping track of the angle of rotation of the sloped face of the bit and/or the teeth.
According to another known system, a transmitter or sonde mounted in a tubular housing is mounted behind and adjacent to the bit and sends a signal that indicates the angle of rotation of the bit. The sonde is mounted in a predetermined alignment relative to the steering portion of the bit. Since the sonde housing is generally made of steel, a series of longitudinal slots or windows are provided through the wall of the sonde housing to permit transmission of the signal. See generally Mercer U.S. Pat. Nos. 5,155,442, 5,337,002, 5,444,382 and 5,633,589, Hesse et al. U.S. Pat. No. 5,795,991, and Stangl et al. U.S. Pat. No. 4,907,658. Mounting of the sonde in its housing has been accomplished by end loading as illustrated by the foregoing patent to Stangl et al. or through a side opening which is closed by a door or cover during use, as illustrated in Lee et al. U.S. Pat. Nos. 5,148,880 and 5,253,721.
Prior attempts to use sondes in horizontal directional boring apparatus, particularly of the type for drilling consolidated rock formations, have proven less than ideal. Breakage of the sonde is to be avoided because sondes are difficult and expensive to replace. The sonde housing cover in side-loading sonde housings is prone to failure. The bolts used to secure the cover often loosen or break off as a result of the abrasion and stress applied to the sonde housing during boring, and the door or cover may work loose or collapse inwardly, crushing the sonde. A need remains for a more secure side-loading sonde housing which is nonetheless easy to open and close when necessary.
A need also persists for a directional boring system specifically adapted to horizontal boring through rocky formations, i.e., wherein the drilling head efficiently bores through consolidated rock formations which ordinary duckbill type bits are unable to penetrate. This can be particularly troublesome when mixed conditions are encountered during a bore, for example, the first portion of the bore is made through soft soil, but an unexpected rock formation is encountered. The connection between the bit and sonde housing should pass torque without undue strain, resist the unavoidable abrasion of surface metal that occurs during use, and yet readily permit disconnection, such as at the terminal end of a bore, at which point the drilling head (including both sonde housing and bit) is typically removed so that the drill string can be used to pull a pipeline back through the completed bore as it withdraws.
Threaded connections between the bit and the sonde housing are secure and shielded from abrasion, but difficult to disengage manually due to the high torque applied to the bit during operation. Bolts used to attach the bit to a sonde housing are exposed to abrasion and tend to loosen. It is also desirable to provide a bit which can be rebuilt and used several times, doubling or tripling the service life of the unit. The present invention addresses these concerns.